A chain saw includes a power head having a drive shaft that drives a sprocket and a guide bar having a peripheral guide edge. The guide bar is mounted relative to the sprocket so that a loop of saw chain is guided in a path from the sprocket onto the guide edge of the bar (a groove in the periphery of the bar). The guide path continues around the nose of the bar in an oval-like pathway that leads back along the opposite side edge of the bar and back onto the sprocket. Because of the forces applied during cutting, the chain is required to tightly fit around the sprocket and guide bar to avoid having the chain jump free of the sprocket and/or bar edge.
Typically the bar is mounted so as to have limited sliding movement toward and away from the sprocket. A screw and nut assembly on the power head controls the sliding movement and a clamping member clamps the relative position of the bar when the desired tension is obtained.
When mounting a chain onto the bar and sprocket, the clamping member is loosened and the screw and nut assembly is manipulated first to allow mounting of the chain and then to tension the chain, at which position the clamping member clamps the bar in that position relative to the sprocket. Unfortunately that is not the end of the tensioning procedure. During operation of the chain saw, the chain develops slack either due to stretching and/or wearing of the components or perhaps due to some slipping of the bar relative to the clamping member. Repeatedly during operation of the chain saw, the operator will have to stop cutting, un-clamp the clamping member, manipulate the screw and nut assembly (typically located on the opposite side of the bar) and re-clamp the clamping member.
As consumer saws have become more and more popular (as compared to professional saws used by loggers), the process of chain tensioning has become more of a problem for the operator. The operator often doesn't remember the process or will attempt manipulation of the screw and nut assembly without releasing the clamping member. This can result in stripping the threads or otherwise damaging the assembly. At the least, the process is seen to be time consuming and a source of frustration to the consumer/operator. It is accordingly an object of the present invention to simplify the chain tensioning procedure to make it safer and more convenient without adding significant cost to the manufacture of the chain saw.